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'using page 0 registers on page 1'
1995\07\01@042016 by Andrew Warren

Edward Cheung ( wrote:

>[Quoting me:]
>>AND the assembler will
>>give you warning whenever you accidently treat a page-0 register as
>>though it were on page 1.
>This does not verify that you have set the page bit right?  It only
>makes sure you don't use the wrong variable name.  Thus if you wanted
>to say :
>but instead typed
>The mechanism you mentioned (XORing the variable name) will catch
>this type of error only.  Is my assumption correct.


Hope you don't mind my copying this reply to the list... It may be
useful to others.

Yes, your assumption is correct; the page bits still need to be set
properly.  Currently, I'm using a VERY complicated (well, complicated
to create, anyway... they're totally invisible when used) set of
instruction-redefining MPASM macros to take care of the page-selection

The example you give isn't the best (although the "xor" will catch that
error); a much-more common error occurs when you're using a part whose
general-purpose registers aren't shadowed in all register banks (e.g.,
16C57, 16C74, etc.), and you simply forget which bank a register is in.

For instance:

   REG1    EQU [any page-0 register]
   REG2    EQU [any page-1 location]


   BSF     STATUS,RP0      ;Switch to page 1.

   MOVF    REG2^080H,W     ;Copy the contents of REG2 to REG1.
   MOVWF   REG1^080H       ;

   BCF     STATUS,RP0      ;Switch back to page 0.

In this case, MPASM will generate a warning on the REG1 access.  If
we'd used "&07FH" instead of "^080H", no warning would have been


Andrew Warren -
Fast Forward Engineering, Vista, California

1995\07\03@081106 by Edward Cheung

>Hope you don't mind my copying this reply to the list... It may be

Not at all.

Thanks for your clarification on the page switch idea.  I had originally
skimmed over your post to the list, thought it was a great idea, and then
filed it away for later study.  When I did study it, I was a little confused
and asked you the question.  That is why I sent you two notes.

I still think your idea is brilliant.

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